How to hook JL F112 sub to both preamp and pre/pro

JL Audio does not support that type of multiple connection, as you know, and I don't think you can get what you want with one sub. I think you probably need to get a sub crossover, Bryston 10b, or 2 way Marchand 44, and run your speakers full out. Set up the Pre/pro with no sub but full range speakers it will send all info including the LFE, through the HT theater bypass to the 2 channel preamp. When you output from your 2 channel preamp to the crossover, it will output all of the lowest frequencies to the sub from both LFE and music to the sub. So if your speakers go down to 40 hrz, you would probably crossover through the electronic crossover at about 45 - 50 hrz with a set slope, testing and listening for the best settings of course, until you get it perfect. All of the LFE effects will come through the sub without damaging the speakers.

texas, are you sure you can't connect both a 2 channel preamp and a HT pre/pro to a fathom sub simultaneously? i was running this setup for a while (on the advice of JL Audio) without any issues. RCA from the HT pre/pro; XLR from the 2 channel preamp. XOver in the HT Processor was set higher than that in the sub. worked great.

Srosenberg, assume your preamp had two sets of outputs for L/R? Also, would assume that one has to be careful not to send signals from both preamp and pre/pro simultaneously, LOL. Seriously though, if that was done in error, could it damage the sub?

I do this right now with an Epik Valor sub.

RCA from the AVR to the LFE input and L/R Line level from my MF A5 Int amp L/R preouts.

For Movies, the A5 is put in the HT Bypass and the preouts become disabled and the AVR drives the sub via the LFE input. Bass Management is via the AVR.

For Music, I turn off the AVR, and use the MF A5 with source components - and the sub is driven from the A5 L/R preouts. "Bass Management" is via the xover cutoff on the back of the sub.

Works just fine.

No, you cannot, you absolutely can get competing signals that can damage the amp/crossover.

I have talked with JL Audio (and Velodyne, and B & W, and Sunfire....) about multiple inputs when I owned an F113. I bought a Rel B1 and sold the JL Audio so I could use one sub for both, with 2 sets of connection. Definitive Technology Subs do this as well.

I really think it's easier, and prob a better set up for a high end system, to buy an external cross over and keep your bad-ass sub like the JL Audio. You are integrating the 2 channel sub anyway, this just take it the next step and takes the lowest frequencies away. If you have speakers that truly go down below 30hrz, you may not want to do that, but then you can just let the full LFE signal go to those speakers anyway without damaging them, and you don't need any connection but the 2 channel, with the processor set to no sub.